In order to adjust optical properties (such as the reflectance and the transmittance) of a glass substrate, formation of a thin film of an inorganic oxide on a glass substrate has been conducted.
As a method of forming a thin film of an inorganic oxide at a low cost, a method has been known wherein a coating liquid containing a precursor to be an inorganic oxide by thermal decomposition is sprayed over a glass substrate at high temperature so that the precursor is thermally decomposed to form a thin film of an inorganic oxide on the glass substrate. The thin film having a low reflectance and a high transmittance to be formed by this method is theoretically preferably a thin film consisting substantially solely of silicon oxide (hereinafter referred to as a silicon oxide film) in view of the refractive index.
However, even if an organic silicon compound alone is contained in the coating liquid, no silicon oxide film is formed at all, or the organic silicon compound is formed into white particles, and no product preferred as a commercial product will be obtained (paragraph [0007] in Patent Document 1).
Accordingly, in Patent Document 1, a specific organic metal compound (an organic titanium compound, an organic zirconium compound or an organic tin compound) to increase the reactivity of a low molecular weight organic silicon compound is added to the coating liquid. According to Tables 1 and 3 in Patent Document 1, the refractive index of the thin film is from 1.55 to 1.71.